Method for injection molding a multi-layer preform for use in blow molding a plastic bottle

Abstract

A method of injection molding a multi-layer preform from a combination of virgin and recycled plastic such as PET so that the resultant blow-molded bottle has a reduced tendency for bottom failure in spite of the use of recycled plastic. A first plastic preform for providing the inner layer of the multi-layer preform is provided with spaced channels on the exterior surface of a closed end thereof extending from a central region of that end to the sidewalls. An injection mold cavity is provided with a like plurality of channels formed therein in a closed end thereof communicating with the injection gate of an injection molding apparatus. The first plastic preform is inserted into the injection mold cavity with the respective channels of the preform and the injection mold cavity substantially aligned. A second layer of plastic material is overmolded onto the first layer by injection molding in the cavity. A third layer of plastic material may be overmolded on the second layer to form a three-layer preform. Preferably the first and third layers are formed from virgin plastic and the second layer is formed from recycled plastic.

What is claimed is: 
     
       1. A method of injection molding a multi-layer plastic preform to be blow molded into a container comprising the steps of: forming an inner layer of a preform of a first plastic material having an open end, sidewalls, and a closed end, said closed end having a plurality of spaced channels on the exterior surface thereof extending from a central area on the closed end to the sidewalls.   providing an overmolding mold cavity defined by sidewalls, an open end for accommodating a core rod, and a closed end with an injection gate therethrough, and a plurality of channels on the interior surface of the closed end communicating with the gate and extending from the gate to the sidewalls;   inserting a core rod and the inner plastic layer of the preform into said overmolding mold cavity with respective channels of the inner plastic layer of the preform and the overmolding mold cavity substantially aligned; and   overmolding a second layer of a second plastic material on the inner plastic layer of the preform to form an overmolded multi-layer perform in said overmolding mold cavity by flowing the second plastic material from the gate only through the respective channels to the sidewalls of the overmolding mold cavity thereby limiting the second material in the closed end of the multi-layer preform to regions of the channels, and wherein the first plastic has a higher resistance to stress cracking than the second plastic.   
     
     
       2. The method of claim 1 wherein the first plastic is PET with a given first IV, and the second plastic is PET with a second IV, the first IV being greater than the second IV. 
     
     
       3. The method of claim 1 wherein the first plastic is virgin plastic and the second plastic is recycled plastic. 
     
     
       4. The method of claim 3 wherein both the first and second plastics are PET. 
     
     
       5. The method of claim 4 wherein the first plastic is PET with an IV from about 0.70 to about 0.86 dl/g, and the second plastic is PET with an IV from about 0.63 to about 0.72 dl/g. 
     
     
       6. The method of claim 1 wherein the first plastic is PET and the second plastic is an injection moldable thermoplastic other than PET. 
     
     
       7. The method of any one of claims 1 or 2 to 3 wherein the respective channels in the inner plastic layer of the preform and the overmolding mold cavity are dimensioned to provide laminar flow from the gate to the sidewalls. 
     
     
       8. The method of claim 7 including the further steps of: removing the overmolded multi-layer preform from the overmolding mold cavity;   providing an additional overmolding mold cavity defined by sidewalls, an open end for accommodating a core rod, and a closed end with an injection gate therethrough;   inserting a core rod and the overmolded multi-layer preform into said additional overmolding mold cavity; and   overmolding a third layer of plastic material on the multi-layer preform in the additional overmolding mold cavity.   
     
     
       9. The method of any one of claims 1 or 2 to 7 including the further steps of: providing an additional overmolding mold cavity defined by sidewalls, an open end for accommodating a core rod, and a closed end with an injection gate therethrough;   inserting a core rod and the overmoleded multi-layer preform into said additional overmolding mold cavity; and   overmolding a third layer of plastic material on the multi-layered preform in said additional overmolding mold cavity.   
     
     
       10. The method of any one of claims 1 or 2 to 7 wherein the forming of the inner layer of the plastic preform comprises the steps of: providing a first mold cavity defined by sidewalls, an open end for accommodating a core rod, and a closed end with an injection gate therethrough, and a plurality of spaced ribs on the interior surface of the closed end and extending from the gate to said sidewalls; and   molding the inner plastic layer of the plastic preform in said first mold cavity by injecting a first plastic material through the gate and between the ribs forming said spaced channels in the resulting closed end of the inner plastic layer of the preform.   
     
     
       11. The method of claim 10 wherein the channels on the exterior surface of the closed end of the inner layer of the preform and the channels on the interior surface of the closed end of the overmolding mold cavity are equally spaced on the respective surfaces thereof. 
     
     
       12. The method of claim 11 wherein there are four channels on each surface spaced by about 90°. 
     
     
       13. The method of claim 1 wherein the channels on the exterior surface of the closed end of the inner layer of the preform and the channels on the interior surface of the closed end of the overmolding mold cavity are equally spaced on the respective surfaces thereof. 
     
     
       14. The method of claim 13 wherein there are four channels on each surface spaced by about 90°.